While increasing energy efficiency has considerable benefits, significant barriers exist. Efficiency potential is spread throughout millions of individual homes and businesses, requires upfront investments and shows returns only over time. This makes efficiency no one’s first priority.

Phytoplankton are microscopic, free-floating plants that form the basis of the aquatic food chain. They also account for half of all photosynthetic activity, and thus produce much of the atmosphere’s oxygen. Changes in the level of phytoplankton activity would have important implications on the health of the entire ecosystem, including human life.

Since the Endangered Species Preservation Act was signed into law in 1966, local and global endangered species lists have emerged as useful tools for protecting threatened animal and plant populations. Prioritizing resources is essential, however, and local situations don’t always reflect global realities — a species could be threatened in one area but plentiful overall, or locally plentiful but in danger worldwide.

Since the 2001 invasion of Afghanistan and the 2003 start of the Iraq war, hundreds of thousands of U.S. soldiers have served increasingly long and difficult deployments overseas. Beyond the physical risks troops face, their absence can have significant negative impacts on family members.

The rise of antimicrobial-resistant bacteria is among the greatest emerging public health problems. Resistance, acquired by bacteria through natural selection, has been accelerated by the improper use of antibiotics. Because such strains can be resistant to even newer, more powerful compounds, their infections are associated both with higher disease and death rates and with greater economic tolls on health care systems.

On September 19 BP’s Deepwater Horizon well was officially declared sealed after having poured nearly 5 million barrels of oil into the Gulf of Mexico. Coincidentally, the following day the National Bureau of Economic Research announced that the recession that started in late 2007 had ended in June. While these two crises are now ostensibly over, their effects are likely to be felt for years.

Televisions entered U.S. households in large numbers after World War II, and personal computers became widespread in business in the 1980s. With these technological innovations, leisure and then work time in the United States began to increasingly center on screen-based systems. Millions of people now spend workdays in front of computers and then retire to their houses to watch TV, play videogames or surf the web.

The 2010 U.S. Patient Protection and Affordable Care Act bears a number of similarities to the Massachusetts health care reform enacted four years earlier. Among them is a requirement that individuals buy insurance coverage or pay a fine, sometimes referred to as an “individual mandate.”

Violent sexual crimes against women continue to represent a devastating social problem that, because of the social stigma and deep cultural biases, often remain under-reported. Globally, one in four women will likely experience sexual violence by an intimate partner and one in three girls report their first sexual experience being forced, according to the World Health Organization (WHO).